Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/bpf/Makefile b/tools/bpf/Makefile
index 53b60ad..5d1995f 100644
--- a/tools/bpf/Makefile
+++ b/tools/bpf/Makefile
@@ -12,7 +12,11 @@
 CFLAGS += -Wall -O2
 CFLAGS += -D__EXPORTED_HEADERS__ -I$(srctree)/include/uapi -I$(srctree)/include
 
-ifeq ($(srctree),)
+# This will work when bpf is built in tools env. where srctree
+# isn't set and when invoked from selftests build, where srctree
+# is set to ".". building_out_of_srctree is undefined for in srctree
+# builds
+ifndef building_out_of_srctree
 srctree := $(patsubst %/,%,$(dir $(CURDIR)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
 endif
@@ -81,10 +85,11 @@
 
 clean: bpftool_clean
 	$(call QUIET_CLEAN, bpf-progs)
-	$(Q)rm -rf $(OUTPUT)*.o $(OUTPUT)bpf_jit_disasm $(OUTPUT)bpf_dbg \
+	$(Q)$(RM) -r -- $(OUTPUT)*.o $(OUTPUT)bpf_jit_disasm $(OUTPUT)bpf_dbg \
 	       $(OUTPUT)bpf_asm $(OUTPUT)bpf_exp.yacc.* $(OUTPUT)bpf_exp.lex.*
 	$(call QUIET_CLEAN, core-gen)
-	$(Q)rm -f $(OUTPUT)FEATURE-DUMP.bpf
+	$(Q)$(RM) -- $(OUTPUT)FEATURE-DUMP.bpf
+	$(Q)$(RM) -r -- $(OUTPUT)feature
 
 install: $(PROGS) bpftool_install
 	$(call QUIET_INSTALL, bpf_jit_disasm)